Fuel injector problem. Stuttering and stalling.

[slicedpi]

I read through some posts with the search function and didn't quite find an answer, though I did learn a couple of things.

I have a rebuilt vortec v6 Z vin in my 93 chevy s10. For probably about a year now I have had an issue where one of the fuel injectors will intermittently stop spraying. I've visually confirmed the injector not spraying (not with a timing light, just my eyes). When this happens the engine stutters and bucks, the rpms vary, and there is a huge loss of power. The fuel injector will kick on and off while this is happening. At first it happened once or twice every 6-8 weeks. Now it is happening weekly, sometimes several times a week. It eventually will stop and return to normal but this takes anywhere from a few seconds to a few minutes. Usually it happens when I start the engine but sometimes it happens while I am driving (shortly after start up). Doesn't matter what the weather is like or if the engine is hot or cold. Once I come to a stop or before I can get it moving it will often stall and there will be a hissing sound. I'm assuming vacuum leak but i've checked with carb cleaner and didn't find anything. I'm quite a noob though and maybe did it wrong.

I also recently changed the spark plugs and coil pack because it was misfiring and hesitating. I had noticed the wires were deteriorating and the spark plugs were black and eroded. Now it is hesitating and misfiring again, sometimes when the fuel injector stops spraying but the two symptoms aren't always together.

I took it to a mechanic and had the codes (OBD1) pulled:

33 MAP sensor
35 idle air control
44 lean exhaust
43 esc module or sensor circuit?

Mechanic said that the fuel injector not spraying was causing these codes. I asked what was causing the fuel injector to fail and he kinda shrugged and said to replace the injectors. Others have said it could be a bad oxygen sensor or MAP sensor.

Could it be that bad sensors are causing the injector to not spray? Should I start by replacing the injectors or the sensors? Note that the injectors and sensors are from the old engine. From reading through the other posts that had similar sounding issues it seems that I should check the fuel pressure. I have not done this yet, not sure how to do it. I did replace the filter a little over a year ago and the fuel pump does prime.

Thanks in advance for any help and insight!

[Rick Norwood]

You said you replaced the plugs and wires, however, did you replace the Distributor Cap? Here is the weird thing about these Trucks. If you replace the Dist. Cap You have to use AC-Delco Only. Nothing else will last more than a few months. You may indeed have an Injector issue, but some of the symptoms sound like My 2000 Jimmy when the Distributor Cap went bad. AC-Delco Dist. Caps aren't cheap, but if you're seeing any P0300 codes, or the inside of the cap is pretty burnt, or visible cracks, holes etc. try replacing the Cap.

[Levithan9]

If you can...ohm out the injector when its cold. Normal values should be 12-18 ohms at 70 degrees....+/- a few for tempature variance.

[slicedpi]

Originally Posted by Levithan9

If you can...ohm out the injector when its cold. Normal values should be 12-18 ohms at 70 degrees....+/- a few for tempature variance.

Both injectors came in at 1.7 ohms, cold. I also noticed both injectors have a leak in the spray pattern when at idle.

[Levithan9]

Time to replace your injectors.

I've seen a lot of the older pintle style injectors take a crap randomly. They have a bad design flaw. And at 1.7 ohms, they defiantly need to be replaced. Older style Lumina had a habit of wiping out a whole bank of injectors if 1 went bad, and at $100+ for each injector....most people scrapped the car.

And since your truck is made by GM.....guess what injector they used to save money? That's right kids.....the same one used in the Lumina.

Replace the 2 bad Injectors.....save up for when the others go bad.

16 years as a auto tech.

[slicedpi]

I actually did replace the injectors on Thursday last week, and the problem is worse with the new ones! It stalls after a few seconds of idle, there is a loud vacuum hiss, and the engine doesn't sound right, like it's struggling for power. I couldn't even test drive it with the new injectors because it stalls at idle. Also noticed that when I give it throttle in park the digital cluster displays random speeds.

So I put the old injectors back in and the truck at least runs. I can drive it. The idle is a little rough, and it hesitates and sputters. So, not sure what to do at this point. The new injectors (BWD, assuming refurbs) also came in at 1.7 ohms so does that mean they are bad? They were $73 each, so maybe I need to get the more expensive ones?

I also took apart, cleaned, and rebuilt the TBI with new gaskets and fuel pressure regulator diaphragm, got a new CTS connector (wasn't reading temp), a new MAP sensor connector, and a new IAC connector. All the connectors were corroded and bad looking. Also replaced all the pre-molded vacuum lines with vacuum hose and a new pcv valve.

[Levithan9]

Does your truck have the "Spider" injector under the intake?

[slicedpi]

no, it's a throttle body. The 220 TBI with dual injectors

[rhandwor]

Are you sure the parts store gave you the correct injectors. I had a friend with a 5.7L who installed 5.0L injectors and it wouldn't idle. I sprayed a little starting fluid in the throttle body and it smoothed out. Then he told me about the injectors.

[slicedpi]

Okay, so it's been running okay for a while, but recently it's been having a problem with hard starting and a rough, low idle. So when it started stalling I replaced the MAP sensor and IAC valve. It ran great for about two days then started stalling again. It stalls as soon as I start it, and I have to give it gas or it just cranks without turning over. Once I get it going I have to give it gas or else it stalls.

I looked at the injectors while it is doing this and they are definitely dripping. When it finally stalls the injectors continue dripping for a few seconds. Is this a problem with the injectors? Or could it be something with the throttle body that houses the injectors?

[rhandwor]

Check for a leaking intake gasket. Spray some wd 40 around the intake,throttle body and vacuum hoses. If it smooths out repair the leak.

[slicedpi]

I made a video to better illustrate the problem: https://www.youtube.com/watch?v=4dEdc1G9Buk

I did try spraying some carb cleaner around the throttle body and vacuum hoses, no change in idle and it still is stalling. The gasket on there is new, just changed them a couple months ago.

[rhandwor]

Originally Posted by slicedpi

I made a video to better illustrate the problem: https://www.youtube.com/watch?v=4dEdc1G9Buk

I did try spraying some carb cleaner around the throttle body and vacuum hoses, no change in idle and it still is stalling. The gasket on there is new, just changed them a couple months ago.

Use a noid light and watch electrical pulse to injectors a wire could be bare and touching a ground or other wire.
Unplug and use ohm meter and check for continuity in wires.
Then put one on good ground and check for ground in wire.
A loose computer ground will also cause these types of problems.
How did you make connections where you spliced wires?
I think you have an electrical problem.

[Tech II]

Where you installed new harnesses, did you solder the connections?

What codes are set? This has flash code capability...

Injectors, when they fail, they fail....they don't get better and run for awhile....you say that, you have periods when the engine runs fine....thus, to me the injectors are ok....

Here is one thing I will try...we definitely see the injector drip when the vehicle stalls......so when it stalls and drips, have someone start the car, remove the harness to the right injector, and when it stalls, does the injector still drip? If it doesn't, there is an electrical problem, and a possible VCM problem....

[slicedpi]

Originally Posted by rhandwor

How did you make connections where you spliced wires?
I think you have an electrical problem.

I spliced them poorly by twisting them together and using electrical tape. I should solder them or use those connectors that you plug the wire into and crimp down. You are not the first to suggest an electrical problem, and I think you are right.

Originally Posted by Tech II

What codes are set? This has flash code capability...

Here is one thing I will try...we definitely see the injector drip when the vehicle stalls......so when it stalls and drips, have someone start the car, remove the harness to the right injector, and when it stalls, does the injector still drip? If it doesn't, there is an electrical problem, and a possible VCM problem....

I flashed the codes and got 35 IAC and 43 ESC. I actually got the codes to clear since my last post by replacing one of the knock sensors. But now they are back. Also, now when I turn the car on the engine light flashes really fast a bunch of times until I engage the tranny, then it flashes more slowly and inconsistently. I tried what you suggested. First of all the injectors are dripping worse now even at idle and while cranking. When I unplugged the right harness it did not stall. Both injectors continued dripping. It's pretty bad.

Also, there is a new symptom: a tick that increases with rpm and only appears when in drive. It is most prominent when the engine is hot. At first I thought it was an exhaust leak because it is more of a puffing sound than a ticking. I had a dislodged gasket once on an exhaust header and that sound was very similar to this one. However, that time it was audible during idle in park. Now it is only audible when driving and hot. And none of the gaskets are dislodged.